Lithium blood levels decreased in the first trimester (−24%, 95% CI −15 to −35), reached a nadir in the second trimester (−36%, 95% CI −27 to −47), increased in the third trimester (−21%, 95% CI −13 to −30) and were still slightly increased postpartum (+9%, 95% CI +2 to +15). Delivery itself was not associated with an acute change in lithium and creatinine blood levels.

Conclusions

We recommend close monitoring of lithium blood levels until 34 weeks of pregnancy, then weekly until delivery and twice weekly for the first 2 weeks postpartum. We suggest creatinine blood levels are measured to monitor renal clearance.